Lecture for students about the application of sputtering technique for deposition of corrosion protective coatings for radiopharmaceutical production.

1. Padua University, 16 September 2013Sputtered thin films for corrosionprotection of targets for radiopharmaceutical production
Anna Skliarova

2. Radioisotope=radionuclideisanatomwithanunstablenucleus.
Canundergoradioactivedecay,resultingintheemissionofγ-ray(s)and/orα-orβ-particles.
2

3. PET-positron emission tomography
3
Radionuclides have wide medical applications:

4. SPECT-single photon emission computed tomography
4
Radionuclides have wide medical applications:

5. Diagnostic
imaging
Therapeutic
applications
5
SPECT/PET-CT

6. Amount of radionuclidesproducedby cyclotrons increases year by year
6
Monthly [18F]FDG activities from January 2003 to August 2011;
there is a >5 fold increase in produced activities over this period.

7. 7
Cyclotron

8. 8
The most used radionuclide in PET [18F]F¯
is produced almost exclusively via
proton irradiation of[18O]H2O
18O
p
18F
n
g

9. 9
Proton irradiation cause water radiolysis
H2O H2, O2, H2O2, ∙OH, H, e- aq,
HO2∙, O2-, HO2-, OH-, H+, …

10. 10
Proton irradiated water
is extremely corrosive!

11. 11
Liquid target structure
Havar® (Co, Cr,Fe,Ni, W,Mo,Mn,C)
Nbbulk

12. 12
Need of corrosion resistant top-coating
onto the Havar®beam window
Havar®foil corroded on beam spot

13. Problem 1:
Proton irradiated Water corrosion
13
Problem 2:
Liquid metal embrittlement
in liquid metal cooling systems

14. 14
Liquid metal embrittlement

15. Problem 1:
Proton irradiated Water corrosion
15
Problem 2:
Liquid metal embrittlement

16. 16
Can be solved by appropriate protective coatings

17. 17
Refractory metals Nb, Ta, Pt, Zr
have extreme chemical resistance

18. Chemical inertness is mandatory,
but not enough
18

19. Microstructurehas a great influence
on corrosion process
19

20. Which film deposition techniquesdo you know?
Which one can provide the microstructure control?
20

21. SPUTTERING
21

22. 22

23. 23

24. 24

25. 25

26. 26
Experimental technique

27. 27
Sputtering system

28. 28
Control panel

29. 29
Sputtering chamber

30. 30
Distance from target to sample –6 cm
•grounded
•No temperature control
•No heating
•No bias
•No plasma cleaning
•liquid nitrogen-cooled
•Cooling by liquid N2
•Possible temperature control
•Possible bias
•Possible plasma cleaning
•No heating
•heated
•Heated
•Temperature control
•No bias
•No plasma cleaning
•water-cooled
•Cooling by water
•Stated temperature
•No bias
•No plasma cleaning
•No heating
Substrate holders

31. 31
Requirement for corrosion protective coatings:
Uniform thickness
Absence of pin-holes
Low porosity
Low diffusion across grain boundaries

32. 32
Analyzing technique

33. 33
Acid porosity test:

34. 34
Acid porosity test: 10% HCl, 30°C, 10 min
1
2
3
4
5

35. 35
Liquid Gallium test: 200 °C, 30 h
a) corrosion b) resistance

36. 36
X-ray diffractometry
2dsinθ=nλ

37. 37
X-ray diffractometry

38. 38
Scanning Electron Microscopie

39. 39
Scanning Electron Microscopie

40. 40
FIB SEM

41. 41
SEM, FIB SEM
SEM
SEM
FIB SEM
FIB SEM

42. Approach to corrosion resistance
42

43. 43
Coating must be dense with minimal distance between grain boundaries
The best possible Diffusion Barriers are Amorphous!
Microstructure requirements:

44. 44
Amorphous films have notypical structural defectsof the crystalline state (dislocations and grain boundaries)
Literature search for corrosion resistance

45. 45
Diffusionthroughtheamorphouslayersisverydifficultduetotheirregularityoftheatomicstructure
crystallineamorphous
long-rangeorderstructurelackoflong-rangeordercharacteristic

46. How to obtain an amorphous film?
46

47. 47
Approaches to obtain an amorphous metal film
Substrate Cooling
Alloying with other elements

48. 48
Experimental results

49. 49
Coating systems investigated:
Nb
Nb2O5
Nb/Nb2O5multilayers
Nb-Ta, Nb-Zr, Ta-Zr

50. Nb
50

51. 51
Parameters investigated for Nbcoatings:
substrate temperature
•-100°C ÷500°C
applied bias
•-150 V ÷+80 V
sputtering gas pressure
•310-3mbar ÷310-2mbar
deposition rate
•0.5 nm/sec ÷5 nm/sec

52. Temperature influence
52

53. 53
Thornton’s Structure Zone Model

54. 4
4
4
4
3
3
3
54
Temperature influence: acid test
Floating
(~250°C)
400°C
500°C
0°C
-100°C
-50°C
300°C

55. 55
40.5 %
-100 °C
40.4 %
0 °C
41 %
Floating
30.04 %
500 °C
-0 %
800 °C
Temperature influence: SEM
Acid test (1÷5)
Optical profilometry(%)

56. 56
4 0.5 %
-100 °C
40.4 %
0 °C
41 %
Floating
30.04 %
500 °C
-0 %
800 °C
Temperature influence: FIB SEM

57. Substrate bias influence
57

58. 58
What happens if substrate is at negative potential?

59. 59
-80 V DC
-400 V DC
grounded

60. DCbias
-80 V
-50V
-80V
-80 V
-150 V
Arpressure, mbar
310-2
510-3
510-2
310-3
310-3
Porosity acid test
3
2
1
1
2
60
DC-biased MS

61. DC-biased MS of Nb:
61
SEM
SEM
FIB SEM

62. 62
All Nbcoatings are columnar!

63. Nb2O5
63

64. 64
Reactive sputtering of Nb2O5:
Sputtering gas pressure
•810-3mbar ÷710-2mbar
Stoichiometry: Ar/O2
•Ar/O2
Applied bias
•-80 V ÷0 V

65. 65
Right Stoichiometry:
25 sccmAr: 19 sccmO2
Nb2O5stoichiometry

66. 66
Liquid Gatest
4
3
1
2
6
7
1
3
2
4
The less porous
6
7
Acid test
▬stoichiometric

67. 67
XRD of amorphousNb2O5:

68. Amorphous Nb2O5deposition recipe:
68
Arflux:
3 sccm
O2flux:
7 sccm
Sputtering pressure:
110-2mbar
IDC:
0.5 A

69. Amorphous Nb2O5:
69
SEM
FIB SEM

70. Nb2O5has superior corrosion protectionbut.. oxides are used to be brittle
70

71. Multilayer Nb/Nb2O5coatings
combine:
highductility & thermal conductivity ofNbwith
excellent barrier propertiesof Nb2O5
71

72. Nb/Nb2O5 multilayers
72

73. thin thick thermal layers layers oxidation
73
M 10
M 10
M 9
M 9
M 8
M 8
M 9
M 10
M 8

74. Multilayered Nb/Nb2O5
(60 nm double-layer) coatings
showedhigh corrosion resistance
74

75. Best Nb/Nb2O5multilayer recipe:
75
Arflux:
3 sccm
O2flux:
0/7 sccm
Sputtering pressure:
310-3/ 110-2mbar
Layer thickness:
40/20 nm

76. 76
FIB SEM
FIB SEM
SEM
Thin Nb/Nb2O5multilayer:

77. Nb-Ta, Nb-Zr, Ta-Zr
77

78. Nb-Ta,Nb-ZrandTa-Zr
were co-deposited in different ratiosin order to find amorphous metallic coating
78

79. Sample holder
79

80. 80

81. Sample-holder for co-deposition
81

82. 82
Stress in thin film

83. 83

84. 84

85. 85
Nb
Ta

86. 86
Nb
Ta
After deposition ~1 μm film
3E-03 mbar

87. 87
Nb
Ta
Compressive stress
Highcompressive stress
3E-03 mbar

88. 88
Nb
Ta
7E-03 mbar

89. 89
Nb
Ta
Tensile stress
Compressive stress
Nb
Ta
7E-03 mbar

90. Mostsuitable sputtering pressure:
90
Nb-Ta
•7E-03 mbar
Nb-Zr
•5E-03 mbar
Ta-Zr
•8E-03 mbar

91. Nb-Ta
91

92. 92
17% Ta
84% Ta
93% Ta
0% Ta
97% Ta
100% Ta
Single target sputtering
Single target sputtering
Co-sputtering
9% Ta
11% Ta
26% Ta
44% Ta
64% Ta
91% Ta
Amorphous-like
110
211
200
Nb-Ta

93. 10-85 %atomic Tain Nb-Taalloy coating lead to amorphous-likestructures
93

94. 94
Acid test

95. 95
12 3 4 5 6 7 8 9 10
Nb↑
Ta↑
Nb
Ta
1
2
3
4
7
5
8
9
6
Nb-Ta

96. Films with higher Ta content are less porous
96
Nb-Ta

97. Nb-Zr
97

98. 98
XRD analysis

99. Acid test
99

100. 100
Sample position
1
2
3
4
5
6
7
8
9
10
Nbcontent, %
93
89
85
79
65
46
29
-
16
7
Acid test (1÷5)
4
1
4
4
3
2
2
2
2
2
12 3 4 5 6 7 8 9 10
Nb↑
Zr↑
1
2
6
3
7
8
4
5
9
10
Nb-Zr5E-03 mbar

101. Porosityis decreasingwith decrease of Nbcontent
101

102. Ta-Zr
102

103. 103
XRD Ta-Zr:

104. Acid test
104

105. 105
Sample position
1
2
3
4
5
6
7
8
9
10
Ta content, weight %
99
98
97
95
90
74
58
32
40
25
Acid test (1 ÷5)
1
2
1
2
2
1
1
2
1
5
1
2
6
3
7
4
5
8
9
10
All samples besides Ta-Zr10, behave quiet good in acid test!
12 3 4 5 6 7 8 9 10
Ta↑
Zr↑

106. 106
SEM of cross-section amorphous Ta-Zr:
Ta50Zr50

107. 107
Not sputtered Havar®substrate
Havar®sputtered with Ta-Zr

108. 108
The best recipes for corrosion protection:
DC-biased or heated sputtering of Nb
Reactive sputtering of amorphous Nb2O5
Nb/Nb2O5thin multilayers
Amorphous Ta-Zr

109. Thank you
for your attention!
109